To understand since it pertains to all routers and configurations that use IP. IP routing is the process of moving packets from one network to another network using routers. To know the routing protocol better you must understand the difference between a routing protocol and routed protocol. A routing protocol is used by routers to dynamically find all the networks in the internetwork and to ensure that all routers have the same routing table. Basically, a routing protocol determines the path of a packet through an internetwork. Examples of routing protocols are RIP, RIPv2, EIGRP, and OSPF.
Once all routers know about all networks, a routed protocol can be used to send user data (packets) through the established enterprise. Routed protocols are assigned to an interface and determine the method of packet delivery. Examples of routed protocols are IP and IPv6.
I am going to show you how to configure and verify IP routing with CISCO routers.
- Routing basics.
- The IP routing process.
- Static routing.
- Default routing.
- Dynamic routing.
Routing Basics
Once you create an internetwork by connecting your WANs and LANs to a router, you'll need to configure logical network addresses, such as IP addresses, to all hosts on the internetwork so that they can communicate across that internetwork.
The term routing refers to taking a packet from one device and sending it through the network to another device on a different network. Routers don't really care about hosts-they only care about networks and the best path to each network. The logical network address of the destination host is used to get packets to a network through a routed network, and then the hardware address of the host is used to deliver the packet from a router to the correct destination host.
If your network has no routers, then it should be apparent that you are not routing. Routers route traffic to all the networks in your internetwork. To be able to route packets, a router must know, at a minimum, the following:
- Destination address.
- Neighbor routers from which it can learn about remote networks.
- Possible routers to all remote networks.
- The best route to each remote network.
- How to maintain and verify routing information.
The router learns about remote networks from neighboring routers or from an administrator. The router then builds a routing table(a map of the internetwork) that describes how to find the remote networks. If a network is directly connected, then the router already knows how to get to it.
If a network isn't directly connected to the router, the router must use one of two ways to learn how to get to the remote network: Static routing, meaning that someone must hand-type all network locations into the routing table, or something called dynamic routing.
Configuring IP Routing in Our Network
It's been correctly configured with IP addressing, administrative
functions, and even clocking(automatically on the ISR routers). But how does a router send packets to remote networks when the only way it can send them is by looking at the routing table to find out how to get to the remote network?. Our configured routers only have information about directly connected networks in each routing table. And what happens when a receives a packet for a network that isn't listed in the routing table?. It doesn't send a broadcast looking for the remote network. The router just discards it.
So we're not exactly ready. But there are servel ways to configure the routing tables to include all the networks in our little internetwork so that packets will be forwarded. And what's best for one network isn't necessarily what's best for another. understanding the different types of routing will really help you.
- Static routing.
- Default routing.
- Dynamic routing.
Static Routing
Static routing occurs when you manually add routes in each router's routing table. There are pros and cons to static routing, but that's true for all routing processes.
Static routing benfites:
- There is no overhead on the router CPU,which means you could possibly buy a cheaper router than you would use if you were using dynamic routing.
- There is no bandwidth usage between routers, which means you could possibly save money on WAN links.
- It adds security because the administrator can choose to allow routing access to certain networks only.
Static routing disadvantages:
- The administrator must really understand the internetwork and how each router is connected in order to configure routes correctly.
- If a network is added to the internetwork, the administrator has to add a route to it on all routers by hand.
- It's not feasible in large networks because maintaining it would be a full-time job in itself.
Default routing
We use default routing to send packets with a remote destination network not in the routing table to the next-hop router. You should only use default routing on stub networks those with only one exit path out of the network, although there are exceptions to this statement and default routing is configured on a case-by case basis when a network is designed. This is a rule of thumb to keep in mind. If you tried to put a default route on a router that isn't a stub, it is a possible that packets wouldn't be forwarded to the correct networks because they have more than one interface routing to other routers. You can easily create loops with default routing, so be careful.
To configure a default route, you use wildcards in both the network address and mask locations of a static route. In fact, you can just think of a default route as a static route that uses wildcards instead of network and mask information.
Example: router(config)# ip route (default ip address) (default subnetmask) ( gateway).
Dynamic Routing
It is when protocols are used to find networks and update routing tables on routers.True, this is easier than using static or default routing, but it'll cost you in terms of router CPU processing and bandwidth on the network links. A routing protocol defines the set of rules used by a router when it communicates routing information between neighboring routers.
The routing protocol I'm going to talk about Routing information Protocol (RIP) version 1and 2, IGRP.
Two types of routing protocols are used in internetworks: interior gateway protocol(IGPs) and exterior gateway protocols (EGPs). IGPs are used to exchange routing information with routers in the same autonomous (AS). An AS is a collection of networks under a common administrative domain, Which basically means that all routers sharing the same routing table information are in the same AS. EGPs are used to communicate between ASes. AN example of an EGP is border Gateway Protocol(BGP).
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